(1) Field of the Invention
The present invention relates to a rotor blade, and in particular to a rotor blade of an aircraft.
(2) Description of Related Art
While moving in rotation, a rotor blade is subjected to a torsor of forces and consequently it is subjected to centrifugal force and also to multiple forces due to flapping movements, to drag, and to torsion. Torsion is caused in particular by changes of pitch seeking to modify the angle of inclination of the blade relative to the plane of the hub supporting the blade. These forces naturally generate bending moments and torsional moments.
The forces and moments to which the blade is subjected and due in particular to centrifugal force and to torsion must then be transmitted to the hub by the blade.
The means for fastening the blade to the hub are therefore subjected to forces and to moments that can be destructive, the term “force” being used below for simplification purposes to designate both said forces proper and moments. Furthermore, it can be understood that it can be difficult to inspect a blade in order to see damage, if any. It is also advantageous to optimize the fastener means in order to limit their weight and in order to reduce the aerodynamic drag they generate in flight.
Document WO 93/08017 describes a blade having a spar subassembly including a retaining element made of metal and of cellular material having fibers braided there about.
Document U.S. Pat. No. 4,302,155 describes a blade provided with a metal base pierced in its center in order to receive a pilot tube. That base includes a cylindrical portion and a portion in the form of a cut defining a cavity, with foam extending from that cavity.
The foam and the base are then covered in fabric forming a rigid skin.
The blade also includes collars for fastening to a hub and clamping onto the rigid skin and the base.
All of the forces to which the blade is subjected appear to transit via the base, with the base being difficult to view because of the presence of the rigid skin.
Other known documents include GB 1 427 158 and U.S. Pat. No. 3,923,422.
The document GB 1427158 describes a blade cooperating with a fitting for fastening to a hub. The fitting includes two cheeks and an opening.